Add ability to set custom MockProviders

[jvanbaarsen]

We have the option to allow users to set their own Query provider instead of Apollo, this works great in production code, but once you're entering testing territory you run into problems.

For Apollo we have a MockProviders function in MockProviders.tsx, this function sets the RedwoodApolloProvider.

To make "Bring your own query provider" more a first class experience we probably want to come up with a solution to be able to either override the RedwoodApolloProvider in MockProviders.tsx, or allowing users to set their own MockProviders.

[jvanbaarsen]

I now fixed it by using this work-around: https://gist.github.com/jvanbaarsen/30a6314e017b01da4a0ad1c4ff98514f.

I can now import this in my tests instead of the render from redwoodjs/testing. This however doesn't feel like a solid solution, and more of a temporary hack.

[dac09]

Thanks @jvanbaarsen for raising this. Pretty valid point! Will try to prioritise next release (v0.32)

[jtoar]

Seems related to #2359.